Polymer ceramic composites are widely used for embedded capacitor application. In the present work PVDF has been used as a matrix and CCTO and LaCCTO have been used as reinforcement. Extrusion process has been used for the synthesis of composites. X-ray diffraction (XRD) patterns confirm the formation of single phase CCTO, and LaCCTO in its pure as well as composite state. It is found that La doping in CCTO considerably increases the dielectric constant and reduces the dielectric loss. A similar trend is observed in the composites with the increasing content of CCTO and LaCCTO.
Recently, polymer ceramic composites have attracted a lot of interest in industrial applications because of dramatic improvement that can be made in their properties by varying the type and amount of dispersion. Modern electronic devices demand new high dielectric constant materials with low dielectric loss and enhanced dielectric strength [
The possibility of developing composites by incorporating ferroelectric ceramics in polymer matrix has been investigated by many workers. Incorporation of ferroelectric ceramic (such as barium titanate, Pb(Mg1/3Nb2/3)O3PbTiO3, and PMN-PT) has been studied by many researchers [
As compared to ferroelectric materials, CCTO has advantage from the application point of view in electronic devices such as capacitors, dynamic random access memories, varistors, and thermistors. CaCu3Ti4O12 has a distorted and complex cubic perovskite-like structure with large unit cell (
Poly(vinylidene fluoride) (PVDF) is a chemically, thermally, and mechanically very stable material. It has excellent ferroelectric, pyroelectric, and piezoelectric properties [
Dang et al. reported a dielectric constant
Most of the researchers remained confined to PVDF-CCTO composites. They focused their study on the dielectric behaviour as a function of CCTO content.
All these studies were confined to dielectric properties. Most of the investigations done so far have reported the dielectric behaviour of the composites containing a very high content of the ceramic fillers. High content of the ceramic in polymer results in the deterioration of mechanical properties due to agglomeration and porosity. In the present investigations efforts have been made to develop high dielectric constant composites at low filler content. In this paper mechanical properties have also been reported along with dielectric properties. Mechanical behaviour is as important as the dielectric properties for applications in the devices.
Poly(vinylidene fluoride) (PVDF) (SOLEF 6008; Ausimont, Italy) with a melt flow index of 24 g/10 min at 230°C under 5 kg load was used as polymer matrix. To synthesise samples of CaCu3Ti4O12 and Ca(1−3
Extrusion process was used to prepare PVDF/CCTO (PVDF-20C) and PVDF/LaCCTO (PVDF-20LaC) composites. Before extrusion, 12 gm of polymer was mixed with 20 wt% of ceramics in a high speed mixer for 30 min. Extrusion was carried out in a twin-screw extruder (Hakke Mini Lab). Mixing was done at 210°C for
X-ray diffraction (XRD) patterns were recorded using a Rigaku Desktop Miniflex II X-Ray diffractometer employing Cu-K
Instron 3369 tensile machine was used for tensile test of dog bone shaped samples at room temperature. A constant crosshead speed of 5 mm/min was selected and the stress-strain data were recorded up to the complete breaking of most samples. Three samples were tested for each specimen.
Contact angle measurements of pure PVDF and composites were done using Kruss (Processor) Tensiometer K 100. The strips were immersed in water at room temperature and the contact angle was measured in the advance mode.
Dielectric measurements were performed on silver coated disc-shaped films of 14 mm diameter. Measurements were carried out in the frequency range 10−2–106 Hz using four-probe Novocontrol setup (ZG4) in the temperature range of room temperature to 80°C.
X-ray diffraction patterns of CCTO, LaCCTO, pure PVDF, and composites are shown in Figure
X-ray diffraction patterns for CCTO, pure PVDF, PVDF-20C, and PVDF-20LaC composites.
Figure
Scanning electron micrographs of LaCCTO, PVDF, PVDF-20C, and PVDF-20LaC composites.
Dog bone shaped samples were made by using injection molding technique (microinjector, model FD-1, Fly Tech Engineering). Temperature of the mould was kept at 70°C and that of the cylinder at 215°C under a pressure of 100 bars. Sample prepared by this method had a cross-sectional dimension of (
Stress-strain curves, Young’s modulus, and elongation ((a)–(c)) for pure PVDF, PVDF-20C, and PVDF-20LaC composites.
Frequency dependence of dielectric constant of CCTO, LaCCTO, and composites is shown in Figures
Frequency dependence of effective dielectric constant of CCTO and LaCCTO (a), PVDF, PVDF-20C, and PVDF-20LaC composites at 40°C (b), at 80°C (c), and at different temperature (d).
Effective dielectric constant of PVDF increases with CCTO and LaCCTO dispersion. For PVDF-20C composite, dielectric constant increases to 24 from 3.5 of PVDF, whereas, in case of PVDF-20LaC composite, dielectric constant is 40. In PVDF-20LaC composite increase in the dielectric constant is quite large. The dielectric constants of the ceramics as well as composites show weak frequency dependence in the range I KHz–1 MHz. This is a desirable from the point of view of application in the devices. With increase in temperature there is an increase in dielectric constant. Increase in the value of
Frequency dependence of dielectric loss (tan
Frequency dependence of loss tangent of CCTO and LaCCTO (a), PVDF, PVDF-20C, and PVDF-20LaC composites at 40°C (b) and 80°C (c).
To predict the effective dielectric constant of the composites various models are used. The dielectric property of a diphasic dielectric mixture comprising spherical crystallites with high dielectric permittivity and a matrix of low dielectric permittivity can be described by Maxwell’s model [
Variation of effective dielectric constant (
In the case of Clausius-Mossotti model [
Experimental values obtained deviate much from the predicted value of
Lichtenecker’s or logarithmic mixture rule is also used to predict the effective dielectric constant value [
Experimental results vary much from the predicted results using this model also (Figure
The effective medium theory (EMT) model [
CaCu3Ti4O12 and Ca(1−3
The authors declare that there is no conflict of interests regarding the publication of this paper.